In the alternative energy field, solar energy holds great promise because it is inherently clean and abundant. Though, solar energy is spatially diffuse so harvesting sunlight poses many technical problems. For example, even in the deserts of the United States, little more than 1 kilowatt of solar energy is present per square meter in the summer. As a result, solar energy utilization schemes typically employ a light collection system that covers a large area. Depending on the nature of this light collection system, solar energy systems frequently become cost prohibitive due to the amount of collection material needed. Additionally, in order to achieve the greatest collection efficiency, light collection systems are generally designed to capture light while the sun changes location in the sky such as by tracking the movement of the sun or utilizing redundant static elements aimed in different directions to enable sufficient collection throughout the day.
Solar energy is commonly converted directly to electricity using photovoltaic (PV) panels. Even though the overall cost of these systems is not competitive with conventional power plants and even though the electricity generated, which is naturally periodic in nature, is not readily stored, the use of solar panels is growing as a result of government subsidies and the ability to push excess power onto the existing power grid, reducing conventional power generation needs. This last capability associated with using the existing grid for “storage” is a way for solar PV systems to side step the problem of storage, but it currently requires the presence of a dominant fuel driven grid.
One way to get around thermal or electrical energy storage issues is to use solar energy to produce a fuel. For example, renewable electricity generated from a solar photovoltaic system may be used to perform electrolysis of water to create a fuel, i.e., hydrogen, which can be stored and transported. Unfortunately, approximately 60 kiloWatt-Hour (kW-Hr) of energy is required to electrolyze enough water to generate 1 kg of hydrogen and because electricity, and in particular renewable electricity, is so expensive water electrolysis is uncompetitive as a process for fuel production.
Another method for utilizing solar energy involves using sunlight to drive a thermal process. One such thermal process involves concentrating the sunlight to heat a fluid which, in turn, can be used to make steam that drives a turbine and make electricity. Except for the fact that it is somewhat possible to store hot fluid for off-cycle power generation, this method lacks a flexible storage method that would allow transportation and later use of the stored energy.
Another type of thermal process uses sunlight to heat a reactor and thereby drive a chemical reaction that produces a fuel, which may be more easily stored and transported. This process may be an effective way to remove the natural periodicity from solar energy production, but, depending on the details of the chemical process that is used to produce the fuel, the required temperatures may be high, necessitating a strong solar concentrator such as a high quality parabolic dish. Traditionally, these have been expensive to produce.